From rift to drift in South Pamir (Tajikistan): Permian evolution of a Cimmerian terrane

Here, we describe the Permian-Lower Triassic sedimentary succession of South Pamir and the associated biota of conodonts, foraminifers and brachiopods. The studied succession comprises the Carboniferous-Lower Permian siliciclastic Uruzbulak and Tashkazyk formations (Bazar Dara Group), which are unconformably covered by upper Lower to Upper Permian units, deposited both in platform settings (Kurteke Formation), and on the slope and basin (Kochusu Formation, Shindy Formation, Kubergandy Formation, Gan Formation, and Takhtabulak Formation). These formations comprise bioclastic limestones, cherty limestones, shales, volcaniclastic rocks, basalts, sandstones and conglomerates, and are locally very rich in fossils (fusulinids, ammonoids, brachiopods, corals and conodonts). The Permian succession is then overlain by shallow water carbonates of the Induan to Anisian Karatash Group. Subsidence analysis and volcanics of the Permian and overlying Triassic successions constrains the timing of rifting of South Pamir from Gondwana in the Early Permian (=Cisuralian), and its docking to Central Pamir, the Eurasian margin and the interposed volcanic arcs at the end of the Triassic. The sedimentary successions of the Pamirs represent a key-point to refine the correlations between the Tethyan regional scale and the International Time Scale. The analyses of the fusulinids and conodonts of the Kubergandian and Murgabian stratotypes of SE Pamir suggest that: (1) the upper Bolorian and the lower part of the Kubergandian correlate to the upper Kungurian; (2) the upper Kubergandian and the lower Murgabian correlate to the Roadian; (3) the mid-upper Murgabian correlates to the Wordian; (4) possibly the uppermost Murgabian and the lower Midian correlate to the lower Capitanian. The Kubergandian is thus a defined regional stage, based on fusulinids, ammonoids and conodonts and can be correlated to the Kungurian and the Roadian; still problematic remains the Murgabian correlation which needs to be investigated and resolved in other Tethyan sections.